Oxidation of olefins to carboxylic acids in the presence of cerium salts and nitric acid



United States Patent 3,407,221 OXIDATION OF OLEFINS T0 CARBOXYLIC ACIDS IN THE PRESENCE OF CERIUM SALTS AND NI- TRIC ACID Eugene F. Lutz, Concord, Calif., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 16, 1966, Ser. No. 602,143 6 Claims. (Cl. 260-413) ABSTRACT OF THE DISCLOSURE Alphaand beta-olefins are oxidized to carboxylic acids by intimately contacting the olefin in liquid phase with an oxygen-containing gas in the presence of an oxidation catalyst consisting of a cerium salt and nitric acid.

The present invention relates to an improved process for the oxidation of olefins to carboxylic acids. More particularly, it relates to an improved process for the oxidation of uand fi-olefins with free oxygen in the presence of a cerium salt-nitric acid mixture as catalyst.

The prior art Catalytic oxidation with molecular oxygen is carried out with different materials under the most varied conditions. Various metals, metal oxides and salts have been proposed as catalysts; nickel, copper, platinum, silver, the oxides of vanadium, zinc, aluminum, as well as the salts of cobalt and manganese, have proved especially effective. The readily controlled continuous catalytic oxidation in the gas phase is often used, e.g., the oxidation of alcohols to aldehydes and acids or to ketones. In some cases, the oxidation in heterogeneous liquid/gas ph ase, in which the oxygen is blown through the reaction materials, has attained technical importance, as in the oxidation of par-aflins to fatty acids or the oxidation of hydrocarbons to peroxides.

Easce, in US. 2,537,577, issued Jan. 9, 1951, discloses a process for the oxidation of a mixture obtained from a conventional oxo synthesis containing, inter alia, aldehydes, alcohols and olefins, using cobalt oleate or other heavy metal soaps as catalysts for air oxidation. According to the process of that patent, the more branched compounds are converted to acids, while the straightin olefins, alcohols and aldehydes are converted to utral compounds.

Various other methods have been proposed for the oxidation of olefins, particularly oxidations involving the use of heavy metal salts. For example, Grinste-ad, in U.S. 3,048,636, issued Aug. 7, 1962, discloses a process for olefin oxidation using thallium (III) salts in aqueous or organic media. The thallic salt is reduced to the thallous form during the oxidation, but the thallous salt must be oxidized separately back to the thallic form for reuse.

Longchain fatty acids in the soap range, i.e., about C to C are important, particularly in the soap-making industry. Many of the naturally occurring acids used in the manufacture of soaps and/or detergents, for example, coconut acids, are often in short supply, while the demand for these acids continually increases. There is, therefore, a need for efiicient methods for synthesizing these fatty acids.

The objects It is an object of the present invention to provide an improved process for the oxidation of mixtures of normal olefins in which the ethylenic unsaturation occurs in the aor B-position along the olefin chain, to carboxylic acids. Another object is to provide a process for the oxidatifi normal olefin mixtures, in which the olefinic 3,407,221 Patented Oct. 22, 1968 compounds contain, for example, from about 4 to about 20 carbon atoms, by providing a catalyst which will selectively oxidize the olefins to carboxylic acids in which the ethylenic unsaturation occurs in the aor B-position. Other objects, aspects and advantages of the invention will become apparent from the following description.

The invention It has now been found that cerium salts, in conjunction with nitric acid, are highly effective catalysts for the selective conversion by free oxygen (or air) of aand t?- ethylenically unsaturated hydrocarbons, i.e., aand ,6- alkenes, to carboxylic acids.

In general, the oxidation can be described by the following equation:

wherein n is an integer from 1 to 18.

The olefin The alkenes oxidized according to the process of the invention are preferably olefins in which the unsaturation occurs in the 00- or ,B-position. However, the charge to the oxidation zone may be mixtures of olefins which are terminally or internally unsaturated, and in which the unsaturation occurs in positions other than the aor 5- position. The olefins may be straight-chain or branchedchain alkenes, and contain from about 4 to about 20 or more carbon atoms in the chain. Example of straightchain olefins which are suitable for use in the process of the invention are propylene, 1- and 2-butene, 1- and 2- hexene, 1- and 2- octene, 1- and 2-nonene, l-decene, 2- decene, l-undecene, Z-decene, and so forth, up to and including 1- and 2-hexadecene, land 2-octadecene, 1- and Z-nonadecene, and 1- and 2-eicosene. Branched chain olefins in which the unsaturation occurs in the 06- or #3- position may also be employed, provided that the branching occurs in other than the fi-position for a-olefins, or in the -position for B-olefins.

In the oxidation, it has been found that the oxidation of a-olefins is most rapid; B-olefins will be oxidized, but at a slower rate than olefins in which the unsaturation occurs in the terminal or alpha position of the chain. Olefins containing internal unsaturation beyond the 5- position, e.g., 3-hexadecene, oxidize very slowly, if at all.

The olefins to be oxidized may be obtained from any conventional source, such as paraffin wax-cracking, paraffin thermal or catalytic dehydrogenation, or growth polymers, such as those from ethylene, by use of the socalled Ziegler aluminum-containing catalysts. The mixture of olefins is preferably predominantly aand B- olefins. The olefin mixture need not necessarily be composed solely of olefins, but may contain substances which are inert or do not adversely affect the reaction, such as parafiins or laldehydes. The olefin mixture may, however, be pretreated to remove the non-olefin constituents.

The catalyst In accordance with the process of the invention, the oxidation of the olefin mixture (i.e., the mixture of 02-, 5-, etc., a-lkenes) is carried out in liquid phase in the presence of a cerium-nitric acid catalyst. Cerium may be charged as either Ce( I-II) or Ce(IV), so long as the cerium-containing compound is soluble in the reaction medium. Cerium salts of either inorganic or organic acids can be used, e.-g., cerous nitrate and cerous acetate. Cerous nitrate is particularly useful because of its high solubility in the solvent employed, and because of its compatibility with nitric acid, its co-catalyst. Other metal salts such as those of vanadium or cobalt or the iron group metals, give very little oxidation to carboxylic acids, yielding primarily nitrated or acetate esterification products.

In general, it is preferred to use substantially less than a stoichiometric amount of catalyst for the oxidation. While the mole ratio of cerium/olefin may satisfactorily be varied between about 1/15 and 1/0.5, it is generally preferred to use a ratio of between about 1/ 1.5 and 1/ 1.0. Within the co-catalyst system itself, mole ratios of cerium/nitric acid of between about 1/ 6 and l/ 0.2, preferably between 1/2 and 1/1, are satisfactory.

The solvent As already pointed out, the oxidation reaction of the invention is carried out in liquid phase in a suitable solvent. The particular solvent employed is chosen based on the solubility of the catalysts therein, and the stability and inactivity of the solvent under the reaction conditions. Parafiins, such as hexane and heptane, are not satisfactory, because of the low solubility of the cerium salts therein. In general, primary and secondary alcohols, likewise, are unsatisfactory, because of their reactivity and tendency to be oxidized. Nitriles, such as acetonitrile and butyronitrile, tend to favor nitration rather than oxidation, and low yields of product acid are obtained.

It has been found that the most satisfactory solvents for the reaction of the invention are the low-molecularweight, especially normal, parafiinic acids, such as acetic, propionic, n-butyric and n-valeric acids. Some ester formation occurs during the reaction, by reaction of the olefin reactants with the paraifin acids, the acids adding to the olefin at the point of unsaturation, thus producing an ester. The ester by-product may undergo nitration, to form a nitro-substituted ester. Thus, the nitration and esterification by-products are the two major contaminants in the acid product.

Because of its availability and low cost, it is preferred to use acetic acid as the solvent. The acid may be used in an essentially concentrated form, or diluted with water; however, it is preferred that the water content of the solvent not exceed about still more preferably 10%, by weight.

The reaction conditions The upper temperature at which the oxidation is effected is limited only by the boiling point of the solvent. For example, when acetic acid is used as solvent, it is preferred to operate at temperatures between about and C.; with propionic acid, temperatures up to about C. are permissible; with butyric acid, the upper limit of the temperature range would be about C.; and so forth. It is preferred, in general, to operate at temperatures above about 100 C., preferably above about 110 C, in order to minimize the reaction time. Temperatures below about 85 C. are conducive to low oxidation yields.

The reaction time is limited not only by the temperature employed, but also by the rate of olefin addition to the catalyst/solvent mixture. It is generally preferred, however, to permit the reaction to continue until at least about 75%, preferably about 85%, of the olefin reactants have been converted.

The oxidation may be run at atmospheric, subatmospheric or superatmospheric pressures. Generally, the pressure is not critical; it is, however, preferred to use pressures between about atmospheric and about 30 p.s.i.g.

In general, the olefin is added slowly to the reaction mixture in order to maintain a low olefin concentration therein, to minimize the formation of by-products.

The following examples are given for illustrative purposes only, and are not to be considered as limiting the invention.

The examples Into a three-neck round-bottom glass flask equipped with a magnetic stirrer was introduced a mixture of cerium (III) nitrate and concentrated nitric acid (70%) in acetic acid. Olefin was introduced dropwise through a dropping funnel through one neck of the flask; a second neck of the flask held a dip tube, through which oxygen was introduced. The third neck of the flask contained a reflux condenser. Table I, below, summarizes the pertinent reaction conditions and product yields obtained from several runs using this apparatus. All runs were made at atmospheric pressure.

TABLE I Rate of 02 Temp., Time, Conversion, Olefin, moles Solvent, cc. Catalyst, moles Addition, 0. hr. percent (basis Remarks cc./min. olefin) l-hexadecenc, 0.1..- Artsigc acid, G gg n 31120, -25 111-114 24 84 SefictviEIOtgHH203(1)121gOgHC=6g)%ii .0 one. 21 u 25 12 HNOa, 0.125. Other=2.9%; 0243 mole acid/mole Do ..do Ce(NOs);-6H;O, -37 114 1. 5 92 0.47 mole acid/mole HNOx.

assas- 31 Do Acetic acid, Ce(NO3);-6HO, -55 113 3. 5 0.42 mole acid/mole HN01.

195. ifigZCF-SJ 4. 0

3, t l-hoxadcccnc, 0.15.... Acgtoic acid, Cefiggge EH20, 55-90 110-114 1 94 solirtiion ieildat rleflux to; 0.5 hr. beigil-e onc. o c 1n :1 1 1on cgun. mo 0 aci HNOs, 0.125. mole 111003. 47.3% N0; recovered. l-hoxadccenc, 0.2.-. Aiggic acid, 015155026 6Hz0, 40 113 l 07 scgctvltgHigggg OHO= 0H0. 27 3 25 7 HN0 0.25. 7.4%; Othcr=2.8%; 413.8% Nbzrccovercd;

0.5 mole acid/mole HNOz. l-octene, 0.3 1 1- 50131805 01518; 61120, 25 108-120 4. 5 27 Sefictevi36+ acl one. 11 a o 4 HNO 0.125. H1C CO0H=9.l4%; Acetic acid= 10.15%; 0.58 mole acid/mole HNOZ. l-octeno, 0.3 Propiong",5 ceagpg snzo, 75 104-118 1g. 75 24. 4 segetvis aci, 0.05 0110. 15 =-;n4

HNO 0.125. H;?3%%O0H=17.8%U; 0.44 mole acid/ mo 0 l-octcnc, 0.3 141513510 acid, C%(g;%3 );lH20, 25 104-111 1 g5 25 segctvgy) Ogl=cfig7fi one. 11 5 v 4 HNOa, 0.125. 4.1%; H1o.ooor1="2.5%; 0.33 mole acid/mole HNOI. l-octene, 0.07 Propilonlii1t C%((I) I37O532;Hz(), 25 116-120 l (2) sellgcttilvgy) 0 am one. n i 2 4 HNO3, 0.125. 5.0%; H1C;COOH= 7.1%; 0.2 mole acid/mole HNOz. 2-octene, 0.2 Acetic acid, Ce(NO3);-6HzO, -25 111 3. 0 (a) 0.08 mole acid/mole HNOz.

112F512? Z-butene, 0.32 Butyric acid, 08610521 61126), -25 110-115 54. a 1.4 fmoletacidlrgole HNO;. A 5 /50 mixturbe 219. 0125+ one. o ace ie an propionic ac s was 0 HNOK, 0.125. tained as acid product.

I Olefin addition discontinued after this time period; second number indicates total reaction time.

2 Only acid portion of product analyzed.

I claim as my invention:

1. A process of oxidizing aand ,B-olefins of from 4 to carbon atoms to carboxylic acids by intimately contacting the olefin in liquid phase with an oxygencontaining gas in the presence of cerous nitrate and nitric acid and in the presence of a low-molecular-weight paraffinic acid solvent in which said catalyst is soluble for a .time suflicient for at least of said aand fi-olefins to be oxidized to carboxylic acids.

2. A process in accordance with claim 1 wherein said oxidation is carried out at a temperature from about C. to about C.

3. A process in accordance with claim 1 wherein the mole ratio of olefin/cerous nitrate is between about l/ 15 and U05.

4. A process in accordance with claim 1 wherein the mole ratio of cerous nitrate/ nitric acid in said catalyst is between about 1/6 and l/0.2.

5. A process in accordance with claim 1 wherein the olefin is an a-olefin.

6. A process in accordance with claim 1 wherein the olefin is Z-butene.

References Cited UNITED STATES PATENTS 2,285,601 6/1942 McAllister 260-533 2,323,861 7/1943 Zellner 260533' 10 2,662,908 12/1953 Logan 260-413 FOREIGN PATENTS 1,243,655 9/1960 France.

15 NICHOLAS S. RIZZO, Primary Examiner.

R. V. RUSH, Assistant Examiner. 

